This invention relates to an environmental-control method for an exposure apparatus and an apparatus which actualizes the goal. Specifically, it relates to the filling method and equipment for filling an inert gas of a specified concentration into a chamber in which a reticle is positioned for an exposure procedure.
As the semiconductor IC becomes more and more integrated, an excimer laser is under consideration for use as an exposure light source for an exposure apparatus in the lithographic process in semiconductor manufacturing. For example, a light source being considered for an exposure apparatus for manufacturing chips of 64 MB DRAM to 256 MB DRAM is a KrF excimer laser of 248 nm wavelength. In addition, in manufacturing chips of higher integration, such as 1 GB DRAM, the use in an exposure apparatus of an ArF excimer laser of 192 nm wavelength is being considered. In an exposure apparatus using the ArF excimer laser and the like as its light source, any portion containing oxygen which absorbs light will have to be purged with an inert gas such as nitrogen or helium which will consequently let the light go through such portion.
In an exposure apparatus, it is necessary to chuck a mask on which a specified circuitry pattern is formed as well as to transfer the mask between the so-called xe2x80x9clibrary,xe2x80x9d mask storage, and a mask stage chamber where the mask is exposed to light. In general, masks are taken to and from the outside of the apparatus through the library. Therefore, it is difficult to isolate the mask stage chamber from the outside. In addition, the mask stage chamber occupies a large volume.
Therefore, replacing air in the mask stage chamber with an inert gas takes a long time. The exposure system of the so-called xe2x80x9cstep and scanxe2x80x9d technique which synchronizes the mask scanning with the substrate movement has a particularly large mask stage chamber. Therefore, replacing air with an inert gas takes an especially long time and requires a large quantity of inert gas. Increasing the amount of an inert gas supplied per unit of time, that is, increasing supply pressure, may reduce the time required for supplying an inert gas to the mask stage chamber. However, there is a limit to increasing supply pressure for an inert gas supplied to the mask stage chamber.
In other words, in general, an exposure apparatus is arranged with a lens system, such as a condenser lens, on top of the mask stage chamber and with projection lenses at the bottom. Therefore, supplying a highly pressurized inert gas into the mask stage chamber pressurizes these peripheral lenses, causing distortion of optical components, thus introducing other problems.
It is accordingly an object of the present invention to solve the aforementioned problems and to provide a method and apparatus which efficiently fills a specified gas into a chamber where a mask or reticle is positioned.
Another object of this invention is to provide an environmental-control apparatus which improves safety during the operation of an exposure apparatus.
To resolve the aforementioned problems in the method incorporating the principles of this invention, a specified gas is supplied to a chamber in which a mask to be exposed is arranged. Part of the air-gas mixture that exists in the chamber is exhausted. After the gas within the chamber reaches a specified concentration, a part of the air-gas mixture is circulated back into the chamber to fill it in with a gas of an appropriate concentration.
The apparatus incorporating the principles of this invention comprises a gas-supplying means which supplies a specified gas to the chamber; an exhaust means which exhausts a part of the air-gas mixture within the chamber and the gas; a detection means which detects the concentration of the gas within the chamber; and a circulation-control means which circulates a part of the mixture within the chamber when the gas within the chamber reaches a specified concentration as determined by the detection means.
In a preferred embodiment, the apparatus comprises mask storage which stores masks to be exchanged with the aforementioned mask;
a mask-transfer chamber which is formed between the mask storage and a mask stage chamber; and
a pressure-control means which sets parameters to satisfy the relationship among (A), the pressure within the mask stage chamber; (B), the pressure of the mask storage; (C), the pressure of the mask-transfer chamber; and (D), the pressure outside the apparatus by fulfilling the following two equations, (1) and (2):
Axe2x89xa7B greater than Cxe2x80x83xe2x80x83(1)
Axe2x89xa7B greater than Dxe2x80x83xe2x80x83(2)
An embodiment of the exposure apparatus may further comprise a sealing means for sealing any space between the mask stage chamber and the transfer chamber when a mask is not passing between them.
The aforementioned circulation-control means may comprise, for example:
a duct for guiding the air-gas mixture within the chamber to the gas-supply means,
a mixing means for re-mixing the air-gas mixture supplied through the duct with the gas, and
a passage-control means for controlling the flow of the mixture supplied via the duct, wherein
the passage-control means guides the mixture supplied via the duct to the air-gas mixing means when the gas within the chamber reaches a specified concentration.
The mixing means may be constructed such that it also acts, for example, as a blowing means which sends a re-mixed gas into the mask stage chamber. Also, the gas-supply means can comprise a blowing means which aids in supplying the gas to the mixing portion, and the passage-control means may comprise a blowing means connected to the duct, and a selection portion which allows the mixture from the blowing means to be selectively supplied to the mixing portion.
An embodiment of the apparatus may also comprise an ionizing means for ionizing at least a part of the gas supplied from the gas-supply means. It also may comprise a steam-supply means for mixing steam with the gas supplied from the gas-supply means.
As described above, in the method and apparatus incorporating the principles of the present invention, because a part of the mixture of a specified gas and the air within the chamber is returned to the chamber and circulated therein, most of the gas supplied to the chamber is recycled, thus reducing the amount of gas supplied. In addition, the mixture begins to circulate at the point when the gas in the chamber reaches a specified concentration, thus, reducing the time required for replacing the air in the chamber with a gas.
Also, because the relationships among the pressures within the mask stage chamber, within a storage area in a mask-transfer chamber, and outside of the apparatus are set as aforementioned, the gas in the mask stage chamber does not flow into the transfer chamber even when a mask is moved into or out of the chamber. Therefore, the purity of the gas in the chamber does not deteriorate, increasing the gas-supply efficiency. In addition, because the gas does not enter the mask-storage area, there is no danger of it being discharged from the storage area.